Easy Stereogram

What is a stereogram? Well I was kind of zoning out on my desktop and I happen to have the same icon several times in a row for some apps and I noticed how my out of focus vision caused them to leap out in 3D.

This is really nothing new, people have toyed with stereograms since 1838 when they were discovered by Charles Wheatstone.

Here is one I made using GIMP:
(also added as an attachment)

1. Start with making a tiled background. The black and white maze pattern was done with Render --> Patterns --> Maze I made a small 140x150 repeating background pattern.
2. Make a row of icons. The Chest are another pattern but the icon spacing is 130 pixels wide.
3. Repeat the step above using a narrower icon. The hats are 120 pixels and again the puzzle square is 110 pixels.

How to use it?
Some people have no trouble throwing their eyes out of focus. The way I do it, look at a single puzzle icon and overlap the blurred until they merge together. Once achieved you should see the puzzle icons in the foreground the hats in the next and the chest in the back just above the background.

How it works?
People with visual impairments affecting one or both eyes can't see the 3D illusion. Most of us have 2 eyes. This is why when we look into the real world each eye sees the world from a slight different angle as the other. The idea behind the stereogram is to show each eye a different image. The brain gets the 2 image maps, interprets them and creates the depth feeling. Your vision is slightly crossed as your left eye is focusing on the 5th icon from the left the right eye is focused on the 4th and the two icons in your brain are the same icon. Since the background of those two are slightly different the brain tells you that the icon must be closer to you than the background.

This is very much like the "single image random dot stereogram" (SIRDS) you can buy at the mall novelty stores. Only they use a gray scale 3D model to change dots in the pattern and make the 3D image pop up.